Process for the production of printing plates



Patented M... 5,1929.

FFICE,

MAX ULLMANN, 0F ZWICKAU, GERMANY, ASSIGNOR TO F. ULLMANN G. M. B, EL, OF

ZWICKAU, GERMANY.

PROCESS FOR THE PRODUCTION OF PRIN TIN G PLATES.

No Drawing. Application filed October 7, 1926. Serial No. 140,215, and in Germany January 28, 1926.

The present invention relates to the production of printing plates suitable vfor use in the off-set process of printing.

One of the-objects of the invention is to produce plates which are free from the defects of printing plates ordinarily used inthe off-set process in that the plates producedsby the present invention are more deeply etched, and etched in such'manner that they are capable of serving as supports for fatty inks.

without the necessity of an intermediate layer between the metal of such plates and the ink.

A further object of my invention is to provide a process of producing these plates in which a sensitized colloid is employed as the resist for the etching process and which colloid is hardened by the presence, in the etching solution, ofsuitable substances which decrease the solubility and prevent the dispergation (i. e. passage into the colloidal dispersed state) of the colloid in said etching solution, so as to prevent under cutting of the colloid during the etching operation.

The etching ingredient employed in such etching solution is of such nature that it will not deleteriously affect the colloid layer, thus making it possible to use a much thinner'and consequently more rapidly printing colloid layer than has hitherto been the case.

It is well known that flat printing plates produced photomechanically by copying from a negative print upon a bichromated albumenized layer will only withstand a limited amount of printing pressure when used in the oil-set printing rocess.

If, for example, such at printing plates as hitherto made are employed for the reproduction of half-tones, especially such as are divided by a fine screen, there arise the disadvantages of ditliculty in printing and of a blurring of the individual dots constituting the screen. These difficulties are primarily caused by the fact that the ink will adhere to the points of said screen as well as to the depressions, thus leading to a blurred and obscure reproduction of the image.

In contrast to the sharp reproduction of the printed images produced on ordinary book-printing machines by means of ordinary half-tone cuts, prints produced by oil'- set printing machines, when using plates preplates as hitherto made were found unsuitable for reproducing the finer screens, as for example screens of from 80 and upwards (1. e. 80 lines per centimeter). Besides the method of producing the printing plates from negative prints for plate printing machines, it is also known that printing plates from diapositives may be produced.

The latter method mentioned was adapted to provide the means for eliminating the inherent defects of the off-set printing plates above referred to. Such printing plates for off-set printing machines are customarily produced by removing the soluble portions of the sensitized colloid layer at the points where it remains soluble after exposure under a diapositive, and thereupon etching the metal parts of the plate thus exposed by the removal of said colloid layer, thereupon the etched portions of the plate were rendered suitable as ink carriers by being filled in with a suitable material.

The sensitized layer which had been rendered insoluble by the exposure Was either directly used as an etching resist or, alternatively, was further protected by a resistive coating superimposed upon said insolubilized, bychromated, sensitized layer. The etching mediums employed were those that hadalready become known in the art of copper-plate printing and the like, and usually comprised either nitric acid or an iron chloride, preferably ferric chlorid, which, as is well known, has an acid reaction when dissolved in water.

The filling in of the etching printing elements of such plates with an intermediate layer, whichis' a characteristic of all existing processes, has avserious disadvantage as Y the filling in of such deeply etched plates is not only quite inconvenient but also causes the obliteration of the finer half-tone divisions in the shadows as well as in the highlights, and a general blurring of the screen, besides being an extra operation which the present invention obviates.

Despite the fact that the hitherto disclosed methods have been known and in use for many years no method had been devised up to the present time for the production of prints in ofiset printing machines which exhibit any apparent advantage in comparison with previous methods of reproduction.

The present invention comprises a novel etching solution containing salts which exert a hardening effect upon the insolubilized sen sitized colloidwhich acts as the resist, while also containing compounds that exert a dissolving action upon the metal of the printing plate. The particular advantages secured reside in a more rapld production of printing plates that exhibit a rich contrast in the images and which are deeply etched by reason of the fact that the etching solution employed is more favorable for deep etching than in the processes hitherto known; and finally in the production of printing plates of such type as have proven extremely resistant to the conditions of use to which they are exposed, and, especially, to pressure exerted thereupon in the printing process. In fact, the plates produced by the present invention are capa tially unlimited pressure without the obliteration of the clear-cut images thereon.

There will now be given an operative example of the met 0d of carrying out the new process, and it is to be understood that other substances that are the chemical equivalents of the materials described in the following example, may be substituted with equal effect, and are to be' considered as strictly within the scope of the present invention.

In order to provide a complete understanding of the invention, the preliminary steps which result in producing the colloid resist are described, although no claim is made for the process of producing the light-hardened, sensitive colloid coating.

Example,

by the light rays. The plate'is then rinsed with water which may be either cold or hot, depending upon the time 6f exposure. This rinsing will remove such portions of the colloid layer as have not been struck by the light rays. In order to render the image visible the same is d ed with an organic dye. After the plate has een dried it is immersed in an etching solution which may have the following composition 200 grams aluminum chloride.

60 grams iron chloride (ferric chloride).

2500 cubic centimeters of water.

The zinc .plate with its adherent insolule of withstanding snbstan-' bilized chromated gelatin layer is immersed in said solution. The aluminum chloride in the solution exerts a hardening and tanning action upon the gelatin upon the zinc plate preventing its loosening from the plate; The

ferric chloride dissolves the zinc of the plate at such points where the surface thereof is not protected by the insolubilized hardened gclatin'layer. By reason of the hardening action of the aluminum chloride the etching of the zinc plate may be carried out much further than has hitherto been found possible, the period of etching being visually followed by periodic examination of the plate in the etching'bath.

After the etching of the zinc plate has progressed to the desired degree, the same is removed from the etching solution, thoroughly rinsed to remove the etching solution therefrom, and then dried; following which a fatty ink is rolled upon the plate. The nature of the fatty ink is such that it will adhere to the exposed metal parts of the plate but will not adhere to the gelatin portions,

but will abut against those portions so that the image will still remain precise and clearout. In other words, the fatty ink now rolled upon the plate will )rotect the metallic layers in the procedure w rich immediately follows.

The plate is then treated with a 4 Beaum solution of hydrochloric acid, and is then rinsed with water. softens the insolubilized bichromated gelatin layer so that after further rinsing the same readily be removed from the plate by bbing it with cotton batting or the like. The printing plate is thereupon brought into condition for printing in the usual manner.

It will thus be seen that the present invention makes it possible to etch the zinc The hydrochloric acid I plate more deeply than has formerly been the a case as any chemicals exerting a pronounced dissolving action upon the zinc usually will be prone to destroy partially the sensitized colloid layer even when the same had been insolubilized b exposure to light, or at least,

to slightly un ercut the edges of such layer so that the outlines of the etched portions are no longer sharp and distinct. In the earlier processes the etching was not carried into the plate at right angles with the surface thereof. The present invention, however, by maintaining perfect contact between the insolubilized colloid layer with the plate and by preventing of undercutting causes the etchlng to proceed substantially at ri ht angles with the surface of the plate so that the outlines will remain sharp and distinct. The prints produced from such plates will be particularly brilliant and clear-cut.

Other salts capable of exerting a hardening action upon the colloid layer, and other equivalent materials ca able of dissolving the metal of the plate without adversely af- 'tected metal of the plate,

fecting the colloid layer, and such materials as are known to those skilled in the art of photomechanical engraving, are to be construed as coming within the scope of the present invention for which the following claims are made.

I claim:

1. In the rocess of producing a printing plate for 0 setprinting in which a lighthardened sensitized colloid layer acts as the resist, the step of etching the unprotected portions of the plate with a solution containing both a salt having a hardening action on said sensitized colloid layer as well as a substance capable of dissolving the unprotected metal of the plate.

2.'In the process of producing a printing plate for ofl set printing in which a lighthardened sensitized colloid layer acts as the resist, the step of etching the unprotected portions of the plate with a solution containing both a salt having a hardening action on said sensitized colloid layer as well as a substance capable of dissolving the unprocarrying the etching of such unprotected portions to such depth that the said portions thereby become capable of directly carrying a fatty ink, the necessity of the intervention of an intermediate ink-carrying layer thereby being obviated.

3. In the rocess of producing a printing plate for oilbet printing in which a lighthardened sensitized colloid layer acts as the resist, the step of etching the unprotected portions of the plate with a solution containing both an aluminum salt exerting a hardening. action on said sensitized colloid layer as well as a solvent for the metal of the unprotected portions of the plate.

4. In'the process of producing a printing plate for offset printing in which a lighthardened sensitized colloid layer acts as the resist, the step of etching the unprotected portions of the plate with a solution contain-' mg both an aluminum salt exerting a hardening action on said sensitized colloid layer as well as a solvent for the metal of the unprotected portions of the plate, carryingthe etching of such unprotected portions to such depth that the said portions become capable of directly carrying a fatty ink without the necessity of the intervention of an intermediateink-carrying layer thereby being ob- .viated.

5. The process of etching metallic printing plates for off-set process printing machines which comprises the use of an etching solution containing a metallic salt having a tanning effect on proteid colloids and a metallic salt capable of etching metals.

6. The process of etching metallic printing plates for off-set printing machineswhich comprises the use of an etchin solution'contalning a metallic salt'capalble of tanning gelatin and a metallic salt having an acid reaction when dissolved in water.

7. The process of etching metallic print-- ing plates for off-set printing machines which comprises the use of an etching solution containing aluminum chloride and an iron salt having an acid reaction when dissolved in water. r

8. The process of etching metallic printing plates for off-set printing machines which comprises the use of an etching solution containing aluminum chloride and iron (ferric) chloride.

In testimony whereof I afiix m signature.

MAX ULiMANN. 

